Switching amplifiers enjoy significantly better efficiency than their non-switching predecessors. However, significant improvements are continuously being made to switching amplifiers to improve fidelity. One recent improvement is the use of multiple references which are selectively switched to a load, often called multi-reference switching amplifiers. Such a circuit configuration is described in U.S. Pat. No. 6,535,058 Multi-reference, High-Accuracy Switching Amplifier, the entire content of which is incorporated herein by reference. Multi-reference switching amplifiers typically comprise an additional regulator than conventional class D switching amplifiers.
A current problem with switching amplifiers involves radio frequency (RF) interference. In order to minimize (RF) interference to surrounding receptors passive output filters using inductors and capacitors are commonly employed after the output stages of multi-reference switching amplifiers. The inductance presented by these filters requires that the regulator control bipolar current at unexpected voltages. This bipolar current requirement is induced by the inductance of the output filters, which places large demands on the regulators used in multi-reference amplifiers, potentially negating the efficiency benefits normally expected from switching amplifiers. In addition, regulators that are capable of both sinking and sourcing current are much more expensive. It would be preferred to use less expensive regulators, which are capable of allowing current to flow in one direction rather than two.
Therefore, a need exists for a method and system where reference regulators of multi-reference switching amplifiers are protected from the bipolar current flow induced by filter inductance.